D.C. cut-off extinguishing ARC circuit

Abstract: When the switch between D.C.power source and load side is cut off, its residual will cause great damage to the life of the switch contact because the air between contact points are ionized. This invention uses a capacitor which is parallelled with the main switch to actuate as a transient shunt so as to improve the residual phenomenon when main switch is cut off.

Description: The present invention relates to a direct current (DC) cut-off switch extinguishing arc circuit. It is known that when the switch between a DC power source and the load is cut off, the residual voltage causes the air between the contact points of the switch to be ionised. As a result of this, such switches are deemed to be inefficient and of relatively low life US Patent 3,739,192 (Oswald) discloses a circuit interrupter for arclessly interrupting current flow to an inductive DC load comprising first and second switches which are functionally offset, in opening sequence, by a predetermined switching interval; during the switching interval, a like level of energy of polarity opposite to the energy stored in the magnetic field of the load is transferred to a capacitor connected in parallel with the first switch, whereupon both energy charges are simultaneously discharged into, and thermally dissipated in, a resistance connected in parallel with the capacitor. According to the present invention, there is provided a direct current cut-off switch arc extinguishing circuit, comprising:- DC power source having two terminals; a cut-off switch and a load connected in series between the two terminals of the power supply, the cut-off switch having first and second contacts; shunt circuit means including a diode and capacitor connected in series between the first and second contacts of the cut-off switch to shunt residual voltage present on the contacts in order to charge the capacitor following opening of the cut-off switch thereby extinguish any arc present when the cut-off switch is opened; and capacitor discharge means for discharging the capacitor to enable it to be recharged and thereby extinguish the arc when the cut-off switch is cut off for a second time; characterised in that the capacitor discharge means comprises a second switch arranged, when closed, to connect the capacitor to a capacitor discharge resistor following charging of the capacitor in order to discharge the capacitor through the capacitor discharge resistor. One form of DC cut-off switch extinguishing arc circuit constructed in accordance with the invention will now be described with reference to the drawings, in which:- Figure 1 is a schematic view of the DC cut-off extinguishing arc circuit; and Figure 2 is a schematic view of a further embodiment of the invention wherein the capacitor discharge means comprises a double switch mechanism. With reference to Figure 1, the present invention comprises a circuit consisting of a DC power source, which may include a pure direct current or a pulsed direct current connected to a load 101 which, as well as being any kind of load, may also be a motor of resisting, electro-inductive or combined type. An electromechanical switch element SW101 is connected in series with the load 101 and in parallel with the DC power source. A diode CR101 is connected in series with a capacitor C 101 according to the order of DC power source polarity, the diode and the capacitor in turn being connected in parallel with the two ends of the electromechanical switch element SW101. A first resistor R101 is connected in parallel with a second resistor R102 which in turn is connected in series with a control switch SW102. The first resistor R101 is in parallel with the two ends of the capacitor C101. In order for the capacitor C101 to discharge at a proper time, the second resistor R102 is in series with an inductive load L101 and the load L101. At the transient time when the main switch SW101 is cut off, the capacitor C101 absorbs the current thereby improving the residual arc around the switch. The stored electric charge of the capacitor C101 is then discharged in order to extinguish the arc when the main switch SW101 is cut off for a second time. In a further embodiment, the first resistor R101 is connected directly in series with the capacitor C101. With reference to Figure 2, a further embodiment of the present invention comprises a circuit consisting of a DC power source, which may include pure or pulsed direct currents connected to a load 201 including all kinds of load or a motor of resisting, or electro-inductive, or combined type. An electromechanical switch element SW201 is connected in series with the load 201, and in parallel with the DC power source. A diode CR201 is connected in series with a capacitor C201 according to the order of DC power source polarity, the diode and the capacitor being connected in parallel with the two ends of the electromechanical switch element SW201. A first resistor R201 is connected in parallel with the two ends of the capacitor C201. For the capacitor C201 to discharge at a proper time, a second resistor R202 is provided in series with an inductive load L201. The diode CR201 is connected in series with the capacitor C201 through a closed contact NC and a dependent contact COM of a flow switch SW202 which in turn is in parallel with the two ends of the electromechanical switch element SW201. The second resistor R202 (and the inductive load L201) are connected between the negative end of the capacitor C201 and an open contact NO so as to charge the residual power energy of the capacitor when the switch is turned to connect the contact NO and the dependent contact COM. The dependent contact COM and the contact NC of the flow switch SW202 must be closed before the electromechanical switch SW201 is switched off, so as to reduce the arcing phenomenon when the electromechanical switch is cut off. In practical use, the DC cut-off extinguishing arc circuit can be structured by series or parallel multiple units. By means of the embodiments illustrated in Figure 1 and Figure 2, one can apply the contact points to a single unit or a multiple unit, including a series of multiple sites for breakers, magnetic switches, manual switches, or over-load cut-off breakers.

Claims: A direct current (DC) cut-off switch arc extinguishing circuit, comprising: a DC power source having two terminals; a cut-off switch (SW101) and a load (L101) connected in series between the two terminals of the power supply, the cut-off switch having first and second contacts; shunt circuit means including a diode (CR101) and a capacitor (C101) connected in series between first and second contacts of the cut-off switch (SW101) to shunt residual voltage present on the contacts in order to charge the capacitor (C101) following opening of the cut-off switch (SW101) and thereby extinguish any arc present when the cut-off switch (SW101) is opened; and capacitor discharge means for discharging the capacitor (C101) to enable it to be recharged and thereby extinguish the arc when the cut-off switch (SW101) is cut off for a second time; characterised in that the capacitor discharge means comprises a second switch (SW102) arranged, when closed, to connect the capacitor (C101) to a capacitor discharge resistor (R102) following charging of the capacitor (C101) in order to discharge the capacitor (C101) through the capacitor discharge resistor (R102). A circuit as claimed in claim 1, wherein the second switch (SW102) has a first contact connected to one end of the capacitor (C101), a second contact connected to one end of the diode (CR101), and a third contact connected to the capacitor discharge resistor (R102). A circuit as claimed in claim 1 or claim 2, further comprising an inductive load (L201) connected in series with the capacitor discharge resistor (R102). A circuit as claimed in any one of claims 1 to 3, wherein the second switch (SW102) is connected between the capacitor (C101) and the capacitor discharge resistor (R102). A circuit as claimed in any one of the preceding claims, further comprising a second load (L201) and a flow resistor (R201) connected in series with the second switch (SW102).

Inventors: YANG TAI-HER, YANG, TAI-HER
Applicants: YANG TAI HER, YANG, TAI-HER
Application year: 1994
Main classification: H01H9
IPC codes: H01H33, H01H9